Sunday, August 13, 2006

SLA battery goof-up

I am trying to share all of the experiences I've had planning for these small DXpeditions, preparing equipment, managing logistics, and so on. It is fun to share my successes but pointing out my mistakes might be just as instructive. So, when I'm an idiot, I will document it in gory detail here. [grin]
I got a couple of 17 Ah sealed lead acid (SLA) batteries from a friend some time ago. Of course I forgot about them for a while and rediscovered them recently. I popped on one of my "smart" SLA two stage chargers to see what happened. Actually, I connected them up and walked away. When I came back later, the little green light was on and I thought, "Great! I'll use those on my next trip!"
Here's a little secret about some of these spiffy little SLA chargers: if the battery voltage is below a certain point, the charger just gives up. So, I wasn't charging these batteries at all. These batteries were dead, dead, dead. I didn't realize this until I had (a) run out and bought new bags to carry them in, and (b) made harnesses for them with inline fuses and PowerPoles. Only then did I realize that one battery was reading 8 volts and the other 2(!) volts. Sigh.
Of course I should have put a voltmeter on these things long before I invested any effort. And, if I were serious about this (and I should be), I would get one of West Mountain Radio's Computer Battery Analyzer (CBA II). A friend has one and swears by it. I should just bite the bullet and get one, too.
In the mean time, I did a cursory web search looking for some cheap Absorbent glass mat (AGM) batteries and found these. The good news is I already have bags and wiring ready when they arrive. I've also got two SLA chargers that will be connected to them trickle charging them constantly. I only need to make that mistake once.
The purpose of these batteries is to give me an opportunity either run nearly forever at QRP levels or even run at 25-30 watts with a larger radio while running portable (like on Georges Island). Of course, at 14 pounds a piece, they chew up my 100 pound budget quickly, but for some trips they'll be well worth it.


Post a Comment

<< Home